Low toxicity primer compositions for reduced energy ammunition

ABSTRACT

A primer composition with reduced toxicity suited for reduced-energy ammunition comprises bismuth (III) oxide as the principal oxidizer and contains a portion of propellant composition mixed therein. This composition may also be used in a cartridge which is otherwise substantially free of any other propellant compound and preferably produces a residue which is substantially free of toxic substances.

FIELD OF THE INVENTION

This invention relates to primer compositions for use in low energy ammunition intended for training and preferably having reduced toxicity.

BACKGROUND TO THE INVENTION

There is an ongoing concern that much of the ammunition produced in the world today contains toxic components, such as heavy metals, that contaminate firing ranges and other locations where ammunition is used in training. In order to reduce the environmental impact from training with traditional ammunition, new compositions that are relatively free of contaminants are sought.

Both the propellant and primer mixtures used in ammunition are potential sources for such contaminants. Various patents disclose propellant formulations that have reduced amounts of contaminants. Formulations for a primer that do not comprise toxic components are described herein.

A particular application for a primer with reduced toxicity is its use in the class of ammunition which may be described as being “reduced-energy” ammunition. Such ammunition is used for training. Examples of such training ammunition are described in U.S. Pat. Nos. 5,035,183 and 5,359,937.

It would be desirable to provide a primer composition to be used in reduced-energy ammunition whereby the primer can serve as an improved source of gases to be evolved and directed to propel the projectile. In certain applications, it would be desirable for a primer to provide a portion of the propellant gases to be used to propel the projectile in combination with providing the primary explosion that is to be used to ignite the secondary explosive, said secondary explosive being used to provide the balance of the primer propellant gases. In another desired application, a second propellant compound need not be present in the cartridge, as the primer composition may also function as the sole source of propellant.

To be effective for the above-mentioned purpose of supplementing or acting as an exclusive source of propellant gas, a primer composition for use in low energy ammunition should evolve a substantial quantity of gas upon ignition.

U.S. Pat. No. 5,417,160 discloses a priming mixture which does not generate toxic oxides upon ignition and has sufficient sensitivity for use with both Berdan and Boxer primers. The primer mix contains a primary explosive, a propellant, a sensitizer, an oxidizer and calcium silicate as the fuel. The preferred oxidizer for this type of fuel is one or more alkaline and alkaline earth nitrates. However, this primer mixture is not intended for use in low-energy ammunition.

U.S. Pat. No. 5,216,199 discloses a lead-free primer composition for rimfire cartridges. The primer comprises diazodinitrophenol, tetracene, propellant, glass and strontium nitrate (as the oxidizer). However, as stated in U.S. Pat. No. '199, “rimfire ignition differs significantly from centerfire ignition so it is apparent that a primer composition which is suitable for centerfire cartridges may not perform adequately in rimfire applications.” Conversely, rimfire primer compositions would not be expected to perform adequately in centerfire cartridges. Additionally, the primer mixture described in this reference is not intended for use in low-energy ammunition.

Finally, U.S. Pat. No. 5,359,937 discloses a cartridge for uses low-energy ammunition having a primer that constitutes the supply of the propellant gas. However, no suggestion is made in this reference of incorporating propellant material in the primer composition.

Other United States patents that make reference to the presence of a propellant component mixed within a primer composition include U.S. Pat. No. 5,831,208 to Erickson (issued Nov. 3, 1998) and U.S. Pat. No. 5,538,569 to Carter (issued Jul. 23, 1996).

A key component of a primer composition is the oxidizer. The oxidizer provides oxygen for reaction with the fuel component. Combustion occurring in a primer is normally expected to generate the high temperatures necessary to ensure that the primer serves its role in igniting the propellant contained in the ammunition.

It would be desirable to provide a primer composition whose ignition products have a reduced toxicity when compared to prior art primer compositions. Bismuth-containing compounds, such as bismuth (III) oxide, are not typically considered to be toxic, in the sense of being substantially more hazardous than simply being irritating to the skin, eyes and respiratory system. Further, the non-solubility and non-hygroscopicity of bismuth (III) oxide are properties that allow this compound to act as a chemically stable component for an explosive.

U.S. Pat. No. 5,654,520 identifies these characteristics as making bismuth (III) oxide suitable for use in forming a delay charge. This patent states that the bismuth (III) oxide composition described therein is able to “burn without substantial gas evolution”. As a component of a primer composition used in a reduced-energy cartridge however, the objective of the reaction is to produce gas.

U.S. Pat. No. 6,227,116 discloses that a metal fuel (such as Al or Ti as a fuel) can be combined with a metal oxide oxidant, identified as bismuth (III) oxide, as one of several preferred oxides, to provide a pyrotechnic train which serves as a detonator for ignition of a secondary explosive.

Neither of these two references address providing a primer composition for an ammunition cartridge.

There remains a need to provide an explosive composition that can be used as a primer compound for ammunition which is chemically stable, generally non-hygroscopic, not substantially soluble in water, provides residual combustion products which are substantially free of toxic materials and which meets the performance specifications required for small caliber ammunition primers in a majority of tests performed according to the standard testing methods.

There is also a need to provide a chemical compound that can be used as a shock-activated gas generant which propels a cartridge that is either a standard cartridge or a reduced-energy cartridge.

Further, there is a need to provide a primer composition which is not adversely affected, particularly overlong storage times, by a water-based marking compound-based payload such as that used in the projectile present in a typical reduced-energy force-on-force training round for small caliber ammunition.

Finally, a need exists for a primer composition which provides a residue which is relatively free of toxic components and which is suited, in particular, for use in low-energy ammunition.

The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.

SUMMARY OF THE INVENTION

According to the current invention, in one aspect, a primer composition to be used in reduced-energy ammunition is provided whereby the primer composition can serve as a source of evolved gases to be directed to propel the projectile. In certain embodiments, a portion of the propellant gases to be used to propel the projectile are provided exclusively by the primer composition. In other embodiments, the propellant component present in the primer supplements a separate propellant present in the cartridge casing.

The primer mixture is preferably characterized by the presence of a percussion initiated, shock-sensitive primary explosive, a combustible fuel, the use of bismuth (III) oxide as an oxidizer and the presence of a further propellant composition mixed with the balance of the primer composition to form the final primer mixture. According to further preferred variants the primer mixture may also include the following constituents, individually or collectively: a secondary explosive, an explosive sensitizer to increase sensitivity to friction/shock and a frictionator which improves the heat generation of the reaction.

According to further variants of the invention, individually or collectively the propellant may be a single- or double based-propellant, the fuel may be a metallic fuel, a binding agent may be included and optional inert filler components may also be present.

Further, and as an additional preferred variant of the invention, the residual products after firing a cartridge containing the primer composition according to the invention are substantially free of toxic elements and components that have historically been associated with cartridge chemistry such as, for example, mercury, lead, barium, antimony, beryllium, cadmium, arsenic, chromium, selenium, tin, thallium as well as similar toxic substances.

According to another aspect, the primary composition of the present invention preferably may comprise: the primary explosive in an amount of from about 20 to about 25% by weight; the secondary explosive in an amount of from 6.5 to about 10% by weight; the propellant in an amount of from about 10 to 20% by weight; the oxidizer in an amount of from about 25 to 40% by weight; the metallic fuel in an amount of from about 5 to 15% by weight; the sensitizer in an amount of from about 2.5 to 5% by weight; and the frictionator in an amount of from about 9 to 11% by weight, such percentages being based on the total of all of the above recited constituents.

More preferably, the primary composition of the present invention may comprise: the primary explosive in an amount of from about 21.5 to about 23.5% by weight; the secondary explosive in an amount of from 6.5 to about 8% by weight; the propellant in an amount of from about 13 to 19% by weight; the oxidizer in an amount of from about 30 to 35% by weight; the metallic fuel in an amount of from about 6 to 10% by weight; the sensitizer in an amount of from about 2.5 to 3.5% by weight; and the frictionator in an amount of from about 9.5 to 10.5% by weight on a similar basis and as similarly presumed hereafter.

Even more preferably, the primer composition of the present invention may comprise: the propellant in an amount of from about 15% to 18.5% by weight.

The propellant is preferably a double-based propellant, that may be selected from the group consisting of nitrocellulose, nitroglycerin, black powder and a mixture thereof. In addition, the propellant may have a mean size of from about 50 to 100 microns. In addition, the primary explosive is preferably diazodinitrophenol; the secondary explosive is preferably pentaerythritol tetranitrate; the oxidizer is preferably bismuth (III) oxide; the metallic fuel is preferably aluminum; the sensitizer is preferably tetrazene; and the frictionator is preferably bismuth powder or titanium powder.

According to a further variant of the invention, the primer composition comprises an effective amount of a binder to maintain the integrity of the primer composition during handling. The binder is preferably a polymerized vinyl compound. It may typically be present in an amount ranging from about 1 to 2% by weight based on the total weight of all of the active ingredients

The primer composition of the present invention is preferably intended for use in a low-energy cartridge having a casing and a projectile. The interior cavity of the casing may either contain additional propellant, or be substantially free of propellant. Furthermore, the projectile in such applications may comprise a reduced weight marking round, which optionally but preferably contains a water-based marking compound.

Diazodinitrophenol (DDNP), also known as “dinol”, is used as the preferred primary explosive and is selected based on its favourable historic performance in other types of reduced-toxicity primers and because it is readily produced from available raw materials.

Pentaerythritol tetranitrate (PETN) was added as a secondary explosive to generate more heat after ignition of the DDNP.

A single- or double-based standard propellant, such as Ball Powder® made by St. Marks Powder, Inc. has been used.

The metal fuel is most preferably provided in the form of aluminum which is a readily available fuel. Titanium and zirconium are possible alternate fuels, but they react very violently and are sensitive to static, making them less preferred for use as fuels in ammunitions designed for training purposes.

Bismuth (III) oxide is used as the preferred primary oxidizer.

Tetrazene is added as an explosive sensitizer to increase sensitivity to percussion.

The frictionator may be an inert granular material, such as glass powder, or it may be a chemically reactive granular material such as bismuth and titanium powder present in an effective amount in order to improve the sensitivity of the primer composition to percussion and to aid with heat buildup of the primary explosive such that the explosive mixture can reach the required explosive temperature. Bismuth powder is preferred over titanium powder as a frictionator due to the handling difficulties of titanium (which may also serve as fuel) However small amounts of titanium (as frictionator) in the primer composition do not lead to the same difficulties encountered when higher amounts of titanium are required to serve as the fuel component. In one embodiment referenced below, titanium powder is used as the frictionator agent.

Binder is optional but preferably provided in an effective amount to consolidate the components and reduce the tendency for the composition to absorb moisture. In this case it was provided in the form of Acronal™, a polymerized vinyl compound. Such a binder may be in the form of any suitable water-soluble composition that does not react adversely with the other components of the invention and will perform its function of consolidating the final primer composition.

The primer composition according to the preferred variants of the invention has demonstrated satisfactory storage life under humid conditions. In some tests a primer according to this formulation, incorporated into a low-energy cartridge and stored in an airtight packaging, was able to perform adequately even after exposure to a high humidity content for months.

The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional side view of a small caliber cartridge comprising the primer composition of the invention and an additional propellant present in the cavity of the cartridge casing.

FIG. 2 is a cross-sectional side view of a small caliber cartridge comprising the primer composition of the invention without any additional propellant being present in the cartridge.

DETAILED DESCRIPTION OF THE INVENTION

References to “toxicity”, as used herein, are to be understood as a relative term. The consumption, use or exposure to large doses of the majority of compounds can, at some level, be determined to be toxic. The compounds of the present invention are said to have a reduced toxicity in comparison with compounds of the prior art which are currently used in primers. In this sense, the disclosed compounds produce a residue after firing that is substantially free of toxic substances. More particularly and preferably, such residues are free of the presence of mercury, lead, barium, antimony, beryllium, cadmium, arsenic, chromium, selenium, tin, and thallium.

Wherever ranges of values are referenced within this specification, sub-ranges therein are intended to be included within the scope of the invention unless otherwise indicated. Where characteristics are attributed to one or another variant of the invention, unless otherwise indicated, such characteristics are intended to apply to all other variants of the invention where such characteristics are appropriate or compatible with such other variants.

The invention is directed towards a primer composition for reduced-energy ammunition with reduced toxicity containing Bismuth(III)oxide as its primary oxidizer. In the present invention, a primer provides a residue which has reduced toxicity. The primer composition is particularly suited for use as an explosive composition in reduced energy cartridges such as those described in U.S. Pat. No. 5,359,937. Such cartridges may contain a small secondary propellant charge or no separate propellant charge whatsoever, relying on the primer composition to produce gasses to be used to propel the projectile.

FIG. 1 depicts a cartridge 1 incorporating the primer composition 2 of the invention, along with additional propellant 4. The cartridge has a head end 5 with an outer casing 3 that slidingly embraces a forward body 6 that carries a projectile 8 at its forward end. When a firing pin (not shown) strikes the head end 5 this activates the primer composition 2 which ignites the propellant 4 allowing propellant gases to flow through the central orifice 9 and the central gas passageway 7 to drive the projectile 8 forward. In this reduced energy cartridge 1, the buildup of gas pressure in the inner casing volume of 10 causes the case 3 to recoil. FIG. 2 depicts a cartridge similar to that of FIG. 1, without the presence of additional propellant. In FIG. 2, the primer composition is the exclusive provider of propellant gases for firing the projectile 8.

Tests have been carried-out establishing the following acceptable ranges and preferred weight percentages for a non-toxic primer composition according to the invention:

TABLE 1 Min. Max. Preferred Component Weight % Weight % Weight % Propellant 10 20 17.5 Fuel (Aluminum) 5 15 7.5 Primary explosive (DDNP) 20 25 22.5 Oxidizer (Bi₂O₃) 25 40 32.5 Secondary explosive (PETN) 6.5 10 7 Sensitizer (Tetrazine) 2.5 5 3 Frictionator 9 11 10

Specific compositions of embodiments of the present invention, by weight percentage, are further provided in Tables 2 to 4. In Tables 2 and 3, bismuth serves as the frictionator, whereas in Table 4, titanium is the frictionator. In addition, three types of propellants were used: Propellant #1 (98.5% nitrocellulose, mean size 50 microns); Propellant #2 (98.5% nitrocellulose, mean size 100 microns); and Propellant #3 (86% nitrocellulose and 12% nitroglycerin; mean size 65 microns).

TABLE 2 Sample No. 1 2* 3 4 5 6 7 8 9 10 11 12 Propellant #1 14.2 10 10 17.5 10 10 17 13.75 12.5 10 12 11.4 Aluminum 10.6 10 7.5 7.5 15 7.5 10 7.5 15 15 10 8.6 DDNP 21 20 22.5 25 25 25 21.5 25 20 22.5 21 22.9 Bi₂O₃ 34.2 40 40 30 30 37.5 31.5 33.75 32.5 32.5 37 34.3 PETN 7 7 7 7 7 7 7 7 7 7 7 8 Tetrazene 3 3 3 3 3 3 3 3 3 3 3 3 Frictionator (Bi) 10 10 10 10 10 10 10 10 10 10 10 11 *In sample 2, the propellant consists of a mixture of Propellant #1, #2 and #3

TABLE 3 Sample No. 13 14 15 16 17 18 Propellant #2 15 10 20 10 15 17.5 Aluminum 10 10 5 10 10 7.5 DDNP 25 20 20 25 25 22.5 Bi₂O₃ 30 40 35 35 30 32.5 PETN 7 7 7 7 7 7 Tetrazene 3 3 3 3 3 3 Frictionator (Bi) 10 10 10 10 10 10

TABLE 4 Sample No. 19 20 21 Propellant #3 15 20 15 Aluminum 15 5 15 DDNP 20 25 25 Bi₂O₃ 25 35 30 PETN 10 7 7 Tetrazene 5 3 3 Frictionator (Ti) 10 5 5

The above components were selected to exclude the toxic components as identified by reference to the standards of the EPA and FBI, as well as particulate and fume toxicity data published by such recognized authorities as OSHA (Office of Safety and Health Administration), ACGIH (American Conference of Government and Industrial Hygienists), NIOSH (National Institute for Occupational and Safety and Health) and COSHR (Canadian Occupational Safety and Health Regulations).

The procedure for preparing a primer according to the invention may be carried out according to the following steps.

A wet mix manufacturing process is preferably adopted for safety reasons. As the ingredients are all substantially insoluble in water, it is advantageous to mix them while they are wet to greatly reduce the likelihood of detonation. The components in their moistened state may then be pressed into primer cups mounted on perforated plates before being sealed and dried in a known manner.

A preferred method of manufacturing the primer composition of the present invention is a batch process wherein the non-explosive components are weighed in their dry form and set aside. The explosive components are each stored separately under humid conditions; the humidity level is measured in order to calculate the dry weight of each explosive component. The wet explosive components are then mixed together; water and an optional binding agent are added to the mixture and mixed. The dry non-explosive ingredients are added and mixed. The batch is stored under humidity until it is ready to be pressed into primer cups.

Table 5 shows standard NATO drop test results to validate the primer's sensitivity to detonation, thus establishing the product's robustness.

TABLE 5 Trial Trial Trial Trial Trial Trial Criteria 1 2 3 4 5 6 H + 5s ≦ 17.70 inches 13.90 13.90 13.45 13.73 11.31 10.97 H − 2s ≧ 2.95 inches 4.43 4.43 5.46 5.57 5.08 4.71 Ho inches 4 4 5 6 4 4

Table 6 shows drop test results conducted at the time of manufacturing, and after six weeks storage in severe conditions of 100% relative humidity and a temperature of 40-45 degrees Celcius.

TABLE 6 Criteria At time of manufacturing After Storage H + 5s ≦ 17.70 inches 16.23 13.29 H − 2s ≧ 2.95 inches 3.95 4.96 Ho inches 4 4

During the course of this project, all steps leading to the identification of a low toxicity formulation for primer compositions were established, including the verification trials of their characteristics, evaluation of their use in reduced energy cartridges and the manufacturing of an experimental lot. Several iterative trials led to a solution of having demonstrated the primer's stability in its packaging for a period of 12 weeks in severe storage conditions. Cartridges comprising the primer of the present invention were tested at various temperatures in US and Canadian rifle and machine gun weapons, including M4/M16, C9/M249 and C7/C8. The combustion of by-products was also determined and analyzed in a confined environment (without air exchange) in order to understand their toxicity. Performance tests results with the cartridges of the present invention were compared with those of prior art cartridges comprising lead primers. The primer composition of the present invention was found to have equal performance characteristics as those with standard lead primers.

CONCLUSION

The foregoing has constituted a description of specific embodiments showing how the invention may be applied and put into use. These embodiments are only exemplary. The invention in its broadest, and more specific aspects, is further described and defined in the claims which now follow.

These claims, and the language used therein, are to be understood in terms of the variants of the invention which have been described. They are not to be restricted to such variants, but are to be read as covering the full scope of the invention as is implicit within the invention and the disclosure that has been provided herein. 

1. A primer composition for use in reduced-energy ammunition primer cup comprising: a) a percussion initiated, shock-sensitive primary explosive, b) a combustible fuel, c) an oxidizer characterized by the use of bismuth(III) oxide as the oxidizer and the presence of a further propellant composition mixed with the balance of the primer composition to form the final primer mixture.
 2. The primer composition of claim 1, further comprising a) a secondary explosive b) an explosive sensitizer, and c) a frictionator wherein the fuel is metallic.
 3. The primer composition of claim 2, wherein the primary explosive is present in an amount of from about 20 to about 25% by weight; the secondary explosive is present in an amount of from 6.5 to about 10% by weight; the propellant is present in an amount of from about 10 to 20% by weight; the oxidizer is present in an amount of from about 25 to 40% by weight; the metallic fuel is present in an amount of from about 5 to 15% by weight; the sensitizer is present in an amount of from about 2.5 to 5% by weight; and the frictionator is present in an amount of from about 9 to 11% by weight, such percentages being based on the total weight of the primary explosive, the secondary explosive, the propellant, the oxidizer, the metallic fuel, the sensitizer and the frictionator.
 4. The primer composition of claim 3, wherein the primary explosive is present in an amount of from about 21.5 to about 23.5% by weight; the secondary explosive is present in an amount of from 6.5 to about 8% by weight; the propellant is present in an amount of from about 13 to 19% by weight; the oxidizer is present in an amount of from about 30 to 35% by weight; the metallic fuel is present in an amount of from about 6 to 10% by weight; the sensitizer is present in an amount of from about 2.5 to 3.5% by weight; and the frictionator is present in an amount of from about 9.5 to 10.5% by weight.
 5. The primer composition of claim 1, wherein the propellant is present in an amount of from about 15% to 18.5% by weight based on the total weight of the active ingredients.
 6. The primer composition of claim 1, wherein the propellant is a double-based propellant.
 7. The primer composition of claim 6, wherein the propellant is selected from the group consisting of nitrocellulose, nitroglycerin, black powder and a mixture thereof.
 8. The primer composition of claim 1, wherein the primary explosive is diazodinitrophenol.
 9. The primer composition of claim 2, wherein the secondary explosive is pentaerythritol tetranitrate.
 10. The primer composition claim 1, wherein the fuel is aluminum.
 11. The primer composition of claim 2, wherein the sensitizer is tetrazene.
 12. The primer composition of claim 2, wherein the frictionator is bismuth powder or titanium powder.
 13. The primer composition of claim 1, further comprising an effective amount of a binder for maintaining integrity of the primer composition during handling.
 14. The primer composition of claim 13 wherein the binder is a polymerized vinyl compound.
 15. The primer composition of claim 1, in combination with a cartridge having a casing with an interior cavity and a projectile.
 16. The primer composition of claim 15 wherein an interior cavity of the casing is substantially free of propellant.
 17. The primer composition of claim 15, wherein the projectile comprises a water-based marking compound.
 18. The primer composition of claim 1, wherein such composition, when fired, provides a residue which is free of toxic substances.
 19. The primer composition of claim 18 wherein such composition, when fired, provides a residue which is free of mercury, lead, barium, antimony, beryllium, cadmium, arsenic, chromium, selenium, tin, and thallium. 